1. Field of the Invention
This invention relates to coated ceramic parts of the type used in manufacturing articles from molten glass, and to a method of fabricating such parts. More particularly, this invention relates to the coating of ceramic parts that are to be submerged, or partly submerged, in molten glass to retard the abrasion of the molten glass contacting surfaces of such parts by the molten glass.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 AND 1.98
In the manufacture of glass articles from a molten glass composition, for example, in the manufacture of glass containers from a molten soda-lime-silica glass composition by a glass container forming machine of the individual section (I.S.) type, various ceramic parts are used at locations where the parts are submerged or partly submerged in the molten glass. Such parts include a ceramic orifice ring, as generally described in U.S. Pat. No. 4,950,321 (DiFrank), which is submerged in molten glass with its upper surface in contact with molten glass, and ceramic glass flow control needles, as identified by reference numeral 32 in U.S. Pat. No. 5,660,610 (DiFrank et al.), and a ceramic feeder tube, as identified by reference numeral 80 in the aforesaid ""610 patent, which are partly submerged, while in use, in molten glass. The aforesaid ""321 and ""610 patents are assigned to the assignee of this application, and their disclosures are incorporated by reference herein.
Molten glass compositions, including soda-lime-silica glass compositions, are very abrasive to the types of ceramic compositions that are used in the manufacture of parts for use, while submerged or partly submerged, in molten glass, and this necessitates frequent replacement of such ceramic parts, orifice rings, for example, typically requiring replacement at 30-60 day intervals, depending on glass color and temperature, and being shorter in high production installations.
It has now been found, however, that it is possible to substantially extend the useful lives of ceramic parts used, while submerged in molten glass, to produce useful articles from the molten glass. The useful lives of the ceramic parts are substantially extended by coating all molten glass contacting surfaces of each article with a superimposed pair of these coatings, each such coating being applied in a fairly thin layer. The innermost or base or ceramic part-contacting coating which need only be applied in an approximate thickness of 0.002 in., is a composite powder coating that is made up of a nickel chromium-aluminum-cobalt-yttria composite powder. Such a coating powder is available from Metco Division of Perkin-Elmer Corporation, whose headquarters are in Westbury, Long Island, N.Y., under their product designation Metco 461. The base coated-ceramic part is then further coated, to an approximate thickness of 0.006 in., with a powder coating that is made up of a prealloyed ceria-yttria stabilized zirconium oxide, which is also available from the Metco Division of Perkin-Elmer Corporation, and this coating powder is offered under the product designation Metco 205 NS powder. It is believed that the base coat, which serves as a bond coat for the top coat, and the top coat for each such coated ceramic part will interact with the ceramic part, after being heated when the part is put into production, to produce a high strength, high resistant coating. Such a coating also produces a thermal barrier between the ceramic and the molten glass, and this thermal barrier protects the ceramic part, to reduce thermal shock thereto and to alleviate the occurrence of cracking.
Accordingly, it is an object of the present invention to provide enhanced life ceramic parts for use, while submerged or partly submerged, in molten glass, in the manufacture of articles from the molten glass. It is also an object of the present invention to provide a method for treating ceramic glass-making parts to extend the useful lives of such parts, notwithstanding that such parts are to be used, while submerged or partly submerged, in molten glass, which is otherwise highly abrasive to such ceramic parts.